To participate in the cooperative approach to the design and conduct of clinical trials in malignant diseases of children. These diseases include leukemia, lymphoma, various solid tumors and other neoplasms to be studied by the Pediatric Oncology Group. These studies will be classified as Phase I for the evaluation of toxicity, tolerated dosage and therapeutic range of new agents or combinations of agents; Phase II, to determine the frequency, extent and duration of remission with new agents and Phase III, to establish the relative efficacy of various therapeutic regimens in neoplastic diseases. Phase I studies will include clinical and experimental pharmaco-investigations such as absorption, plasma half-life, body fluid levels and excretion in man and animal model. To investigate some of the biochemical and biological aspects of the neoplasms under study as they derive from patient material available for the cooperative studies. To actively participate in and contribute to the overall Group effort. This will include scientific input, support in protocol design, chairmanship of studies and other activities called for.